In recent years, studies have been intensively carried out for a light emitting device that uses, as illumination light, fluorescence generated by a light emitting part which includes a fluorescent material. The light emitting part generates the fluorescence upon irradiation of excitation light, which is emitted from an excitation light source. The excitation light source used is a semiconductor light emitting element, such as a light emitting diode (LED), a laser diode (LD), or the like.
Patent Literature 1 discloses a lamp, which is an example of a technique that relates to such a light emitting device. In order to achieve a high-luminance light source, the lamp employs a laser diode as an excitation light source. Since a laser beam oscillated from the laser diode is coherent and therefore highly directional, the laser beam can be collected without a loss so as to be used as excitation light. The light emitting device employing such a laser diode as the excitation light source (such a light emitting device is called an LD light emitting device) is suitably applicable to a vehicle headlamp.
Patent Literature 2 discloses a lamp, which is an example of a technique in which a wavelength conversion material emits visible light upon irradiation of infrared light. The lamp is configured such that the wavelength conversion material is provided at a focal point of a concave mirror, which reflects visible light emitted from the wavelength conversion material. This configuration allows the lamp to serve as a light source. The configuration of Patent Literature 2, in which the wavelength conversion material is provided at the focal point of the concave mirror, is applied to the lamp of Patent Literature 1, which has the fluorescent material provided to a parabolic reflecting surface or to an ellipsoidal reflecting surface.
Patent Literature 3 discloses a lamp, which is an example of the technique that relates to the light emitting device. The lamp contains in its light emitting part not only blue, green, and red fluorescent materials, but also a yellow fluorescent material. This achieves a light emitting device which is excellent in a color rendering property. Further, the lamp of Patent Literature 3 produces a luminous flux of approximately 1200 lm (lumen) and has a luminance of approximately 25 cd/mm2, which are as high as those of a halogen lamp, and is as excellent in a color rendering property as the halogen lamp.
Further, Non Patent Literature 1 discloses a vehicle headlamp, which is an example of a technique for achieving a vehicle headlamp that employs an incoherent white LED.